The present invention relates generally to electrical testing (e-test) and wire bonding for a metallization process flow. More particularly, the present invention relates to an electroless plating process flow that follows e-test, and for a wire bonding process flow that follows a metal-six copper (M6 Cu) metallization.
Metallization process flows may be carried out near the back-end of processing by electrical connections such as a metal bump formation on a ball-limiting metallurgy (BLM) that surmounts the metallization pad, or by a wire bonding process on the metallization pad. During the wire bonding process, typically an aluminum or gold wire is used to make contact with the metallization pad. However, this process flow often causes significant corrosion of the metallization pad, particularly if it is copper, and the result is an unacceptable yield loss during the wire-bonding process. FIG. 8 depicts a prior art wire bond on a metallization pad that illustrates corrosion. A semiconductor structure 10 includes a substrate 12 and an upper metallization 14 such as a trace or pad, that is electrically connected to a lower metallization 16 through a contact 18. A wire bond 20 is depicted in connection with upper metallization 14. It is noted that upper metallization 14, if copper for example, has experienced corrosion 22 (depicted in an arbitrary size and shape).
The corrosion 22 has resulted from at least one of several environments or other conditions. For example, an aluminum wire bond 20 will corrode upper metallization 14, or processing conditions including back-end-of-line (BEOL) testing such as a hot ambient steam test (HAST) and/or burn-in, add to corrosion 22. Other processing conditions add to corrosion including the galvanic differential that is established between the two disparate metals of upper metallization 14 and wire bond 20. Once corrosion begins, a variable and unpredictable contact resistance (CRES) occurs between the numerous probes and the upper metallization 14. Additionally, a copper scumming of the probe tip requires frequent and unpredictable cleaning.